1. Field of the Invention
The present invention relates to the horizontal growth of nanotubes/nanofibers. “Horizontal growth” is used to designate a growth in directions substantially parallel to the plane of a substrate, this growth developing from one or several sides of pad or of a thin layer portion.
The present invention more specifically relates to a connection method usable to form connection planes in the upper layers of an integrated circuit.
2. Discussion of the Related Art
Nanotubes/nanofibers, for example carbon nanotubes or silicon nanofibers, have many applications. One of the currently most common methods for growing such nanotubes/nanofibers is to make them grow from the bottom of a cylindrical cavity. This growth mode is particularly suited to the forming of vertical connections between horizontal conductive regions of connection planes of an integrated circuit.
FIGS. 1A and 1B illustrate steps of the manufacturing of an integrated circuit connection level by a so-called “damascene” technique.
As illustrated in FIG. 1A, it is started from the upper surface of a layer 1 made of an insulating material, at some locations of which metal vias 2a, 2b, 2c, 2d make flush. An insulating layer 4 which is etched to form openings 5a, 5b, 5c is deposited on this structure.
At the step illustrated in FIG. 1B, the openings have been filled with a metal such as copper by first uniformly depositing a copper layer thicker than insulating layer 4, then performing a chem./mech. polishing (CMP) of this layer so that it fills openings 5 formed in layer 4. Copper regions 6a, 6b, 6c have thus been formed. In the shown example, copper layer portion 6a is intended to form a connection between via 2a and a higher-level via 8a distant in top view from via 2a. Layer portion 6b simply behaves as a connection pad between a lower via 2b and an upper via 8b. Layer portion 6c is intended to ensure the connection between vias 2c and 2d, and possibly with a higher-level via 8c. 
As the integrated circuit dimensions decrease, the widths and the thicknesses of metal tracks such as tracks 6a and 6c of FIG. 1B tend to decrease. As a result, it becomes more and more difficult to run relatively high currents through such conductors without causing an excessive warming up, or even a diffusion of the metals into the adjacent layers or, again, a destruction of such conductors.
It has been provided to replace the conductors formed of metal layers with conductors formed of structures such as carbon nanotubes or other nanofibers. However, the practical implementation of such structures comes against many difficulties.